Brazed heat exchangers have enjoyed and continue to enjoy considerable popularity in the heat exchanger art, particularly among manufacturers of lightweight, compact and high performance heat exchangers as used in aircraft. There is growing interest, however, in brazeless heat exchangers, that is, heat exchangers in which means other than metallurgical bonding are used to close and seal the numerous existing joints. It is hoped thereby to avoid problems known in the art, resulting from defectively brazed joints, salt contamination, vibration induced fracturing of brazed joints and like causes. It would be hoped also that an unbrazed heat exchanger would allow access to its tubular core for inspection and servicing. The achieving of these objectives is not obvious, however. The known prior art provides no examples of high density, high performance heat exchangers to which a designer may turn in attempting to respond to the interest in unbrazed constructions.